1. Field of the Invention
The present invention relates to a motion detector assembly that is adapted to be integrated into a decorative coach lantern and more particularly to a motion detector assembly that includes a housing and a sensor carrier subassembly which includes a passive infrared (PIR) sensor and a Fresnel lens, the Fresnel lens being configured in a cylindrical section and disposed generally parallel to a longitudinal axis of the assembly to provide improved optics, such as improved gain and reduced aberrations.
2. Description of the Prior Art
Decorative coach lamps with integral motion sensors are relatively well known in the art. Examples of such decorative coach lamps are disclosed in U.S. Pat. Nos. 5,282,118 and 5,434,764. In such decorative coach lanterns, the motion detector, normally a passive infrared (PIR) sensor, is carried by a housing, rigidly disposed beneath a lamp assembly and configured to blend aesthetically with the overall appearance of the coach lamp. In both the '118 and the '764 patents, the motion detector housing is formed with an upper housing portion and a lower housing portion which when assembled together resemble a decorative housing, rigidly carried on the top or bottom of the lamp assembly.
The lower housing portion of such a motion detector housing is formed in either a convex as disclosed in the '118 patent or a conical shape as disclosed in the '764 patent and includes an annular window, aligned with the sensor within the housing. A multi-faceted Fresnel lens, used to focus the infrared radiation on the PIR sensor, is secured to the annular window. As such, the surface of the Fresnel lens is generally configured in a conical or convex shape. Requiring the Fresnel lens to conform to the shape of the annular opening limits the flexibility of the optical design and can result in reduced performance. Moreover, the design of the Fresnel lens in such a configuration is dependent upon the configuration of the housing.
There are other problems with utilizing motion detector housing assemblies having a Fresnel lens configured in a conical shape as disclosed in the '764 patent or a convex shape as disclosed in the '118 patent. In particular, with configurations such as disclosed in the '118 and '764 patents, it is known that such configurations can cause aberrations which, in turn, decrease the overall gain of the sensor. Furthermore, the '118 patent discloses a convexo-convex type housing for the PIR sensor which requires a Fresnel lens to be formed in a convex shape with curvature along two directions in order to seat against the annular window in the lower housing portion. Such a Fresnel lens would be relatively difficult to manufacture and certainly expensive, thereby driving up the cost of the entire decorative coach lamp assembly.